• The natural growth of a human child requires hCG.pregnancy on red image by starush from Fotolia.com
  
  Human chorionic gonadotropin (hCG) circulates in the body during pregnancy and other conditions. A healthy pregnancy requires hCG to support the embryo's development. Without required hCG, early pregnancy loss or miscarriage occurs.
  
  HCG's dimeric glycoprotein structure forms by combining two identical protein-carbohydrate molecules. Production occurs in the placenta or embryonic liver during pregnancy.
  
  HCG molecules differ in size and complexity. Forms other than intact hCG may indicate the presence of disease or genetic abnormalities.
  
  

Pregnancy

• Human Chorionic Gonadotropin hormone levels rise and then level off in pregnancy.pregnancy image by AGphotographer from Fotolia.com
  
  Intact human chorionic gonadotropin increases in pregnancy. Levels rise quickly during the first 2 months and peak during the first trimester. In the second trimester, hCG levels decline by about 80% from these peaks. Circulating hCG levels vary among pregnant women. Created by the developing fetus and the synctiotrophoblast (the outer layer of the trophoblast), attachment of the fetus to the uterus and nutritional pathway development begins.
  
  Intact hCG molecules have single and two-pronged membrane-coated transport links to sugar molecules and other basic oxygen-linked sugar units.
  
  HCG prevents possible breakdown of the ovary's corpus luteum. The corpus luteum, or yellow body, maintains the endometrium (uterus lining) during pregnancy. A remnant of the human egg, the corpus luteum, produces a crucial pregnancy hormone called progesterone. The corpus luteum makes progesterone until the placenta takes over at around 10 weeks.
  
  Compared to intact hCG, other hCG molecules have more complex structures. More sugar chains, three-pronged membrane-coated transport links, and four-sided carbohydrate molecules suggest other conditions besides pregnancy to doctors.
  
  

Presence of Fetal Down Syndrome

• Sophisticated medical tests determine genetic abnormalities such as Down syndrome.screening image by kromleh from Fotolia.com
  
  Higher than usual amounts of a certain kind of hCG may suggest a Down syndrome in the fetus, although high hCG levels do not confirm Down syndrome. Additional tests can confirm a pregnant woman's risks of delivering an infant with Down syndrome.
  
  Twice as much hyperglycosylated hCG circulates in the blood of a woman carrying a Down syndrome fetus. Very large hGH-H molecules, twice the size of normal, intact hCH, present under the microscope.
  
  HCG-H, produced by cytotrophoblast cells (the inner rather than the outer layer of trophoblast cells), does not stimulate progesterone production, according to studies published by the National Institutes of Health.
  
  Amniocentesis, or testing of amniotic fluid for genetic abnormalities, usually confirms Down syndrome.
  
  

Tumor Sources

• HCG may indicate the presence of cancer.microscope image by Fotocie from Fotolia.com
  
  HCG and other hormones may indicate the presence of cancer. Circulating gastrin, needed to produce hydrochloric or gastric acid in the stomach; prolactin, necessary to product milk in the breast for nursing mothers; calcitonin, produced in the thyroid; corticotropin hormone, formed in the cells of the pituitary gland; and catecholamine, the fight-or-flight hormone released by the adrenal glands; may have a tumor as a source.
  
  

Phantom or No Known Source

• Doctors test hCG levels following some kinds of surgery.main surgeon image by Andrey Rakhmatullin from Fotolia.com
  
  Chemotherapy, or prescription medication to kill cancer cells, or surgery may cause inaccurate hCG test levels. Medication and surgery can be performed to remove hormone-secreting tissue. Even tiny tissue remnants can elevate hCG levels. Follow-up hCG tests confirm removal of secreting tissue. Monitoring hCG levels helps doctors determine the success or failure of treatment. Technicians sometimes refer to unknown variables as phantom sources.
  
  

HCG and Disease

• HCG levels may indicate the presence of disease.doctor image by JASON WINTER from Fotolia.com
  
  HCG levels may also indicate pituitary disease and germ-cell (inside the ovaries and testicles) cancers. Tests for tumor markers, including the presence of some hormones, alerts doctors to perform additional, confirming tests for these conditions.